Make it go when I walk up to it.

June 7, 2012 1:11 PM

I would like to use a motion sensor/occupant detector to trigger scripts in a Linux box. I'm open to using a web cam, building something with an Arduino, modifying a commercial motion sensor, etc.

Here's the scenario: a person will walk up to a door. I would like a sensor to detect their presence, then send that signal to a Linux box. (Could be Windows, I guess. Probably not though.) I'll use the signal to tell the computer when to begin playing audio and video, probably through MAX/MSP.

The less intrusive the device, the better. Pretend cost isn't an issue, although less expensive is always good. Hit me with your best ideas!

posted by nosila to media & arts (2 answers total)

PIR motion detector like this one:

* you can probably wire it directly into a cheap USB keyboard so that when triggered, it pretends to hit a key, which activates your computer thingy. Since the sparkfun PIR sensor has an open collector output, find a point on the keyboard matrix which triggers a keypress when shorted to ground, and connect the output of the sensor to that matrix point and the ground to the ground of the keyboard. You should be able to steal +5v from the keyboard too.

If you want to get fancier, connect the PIR to an arduino and use one of the many arduino-to-MAX-MSP communication libraries.
posted by moonmilk at 1:47 PM on June 7, 2012

A PIR detector was my first suggestion also; they're cheap and small and so on. If you can arrange it so that its field of view is the volume you want to detect, then it's probably ideal.

Small sonar and radar (field disturbance) modules can be had cheaply, which (like PIR detectors) were probably designed for automatic doors / occupancy detectors / the like. For shorter ranges, near-IR (reflection detecting) proximity sensors, and capacitive sensors, might be the way to go. If you want the sensor's trigger point to be more precise, you could use an 'electric eye' beam break sensor, like some stores use to ring the "a customer has arrived" bell. And finally you could buy or make a pressure switch mat (like some supermarket doors use).

If your Linux box has a spare serial port, one of the easiest ways to get a digital input is to attach it to one of the modem-status signals on the port. Otherwise, an Arduino connected via USB is probably easiest.
posted by hattifattener at 2:55 PM on June 7, 2012